This invention relates generally to dipeptides and tripeptides and to methods for pharmaceutical treatment of mammals using analogs of such dipeptides and tripeptides. More specifically, the invention relates to tripeptides and their analogs, to pharmaceutical compositions containing such dipeptides and tripeptides and to methods of treatment of mammals using such dipeptides and tripeptides. In addition, the invention relates to methods of treatment of mammals using such dipeptides and tripeptides for control of appetite, blood pressure, cardiovascular response, libido, and circadian rhythm.
1. Appetite and obesity
Obesity is a major disorder affecting as much as one third of the North American population. Several studies have shown that such individuals are at increased risk in developing cardiovascular disease (hypertension and hypercholesterolemia), diabetes and several types of cancer. The effective treatment of obesity, however, remains a largely unachieved goal. Existing pharmacotherapeutic approaches to weight loss involve the use of amphetamine-based agents such as amphetamine, diethylpropion, mazindol and fenfluramine which act directly on the CNS to lower food intake by modulating dopaminergic, adrenergic and/or serotonergic mechanisms. Although weight loss can be achieved with such agents, their use is restricted due to CNS side-effects, potential addiction liability and the production of tolerance to their actions, with chronic administration leading to potential depression, vestibular disturbances, hallucinations and addiction, as well as interference with the actions other drugs such as MAO inhibitors and antihypertensives. There is also a subpopulation of obese patients that is refractory to present anorectic drug treatments. The medical need is high for an effective anorectic agent which overcomes the above disadvantages of existing therapies. Of particular need are agents which act by alternative mechanisms to modulate food intake and/or metabolism.
2. Neuropeptide Y ("NPY")
Throughout this application, various publications are referenced. The disclosure of these publications is hereby incorporated by reference into this application to describe more fully the art to which this invention pertains.
Neuropeptides are small peptides originating from large precursor proteins synthesized by peptidergic neurons and endocrine/paracrine cells. They hold promise for treatment of neurological, psychiatric, and endocrine disorders (De Wied, D. In: Neuropeptides: Basics and Perspectives (Elsevier, Amsterdam-N.Y.-Oxford), 1990.). Often the precursors contain multiple biologically active peptides. There is great diversity of neuropeptides in the brain caused by alternative splicing of primary gene transcripts and differential precursor processing. The neuropeptide receptors serve to discriminate between ligands and to activate the appropriate signals. Thus, it is expected that the receptors for neuropeptides consist of a large number of members.
Neuropeptide Y (NPY), a 36-anino acid peptide, is the most abundant neuropeptide to be identified in mammalian brain. NPY is an important regulator in both the central and peripheral nervous systems (Heilig, M. and E. Widerlov. Neuropeptide Y: an overview of central distribution, functional aspects, and possible involvement of neuropsychiatric illnesses. Acta Psychiatr. Scand. 82:95-114 (1990).) and influences a diverse range of physiological parameters, including effects on psychomotor activity, food intake, central endocrine secretion, and vasoactivity in the cardiovascular system. High concentrations of NPY are found in the sympathetic nerves supplying the coronary, cerebral, and renal vasculature and has contributed to vasoconstriction. NPY binding sites have been identified in a variety of tissues, including spleen (Lundberg, J. M., A. Hemsen, O. Larsson, A. Rudehill, A. Saria, and B. Fredholm. Neuropeptide Y receptor in pig spleen: binding characteristics, reduction of cyclic AMP formation and calcium antagonist inhibition of vasoconstriction. Eur. J. Pharmacol. 145:21-29 (1988)), intestinal membranes, brain (Hinson, J., C. Rauh, and J. Coupet. Neuropeptide Y stimulates inositol phospholipid hydrolysis in rat brain microprisms. Brain Res. 446:379-382 (1988)), aortic smooth muscle (Mihara, S., Y. Shigeri, and M. Fujimoto. Neuropeptide Y-induced intracellular Ca2+ increase in vascular smooth muscle cells. FEBS Lett. 259: 79-82 (1989)), kidney, testis, and placenta (Dumont, Y., J. C. Martel, A. Fournier, S. St.-Pierre, and R. Quiron. Neuropeptide Y and neuropeptide Y receptor subtypes in brain and peripheral tissues. Prog. Neurobiol. 38:125-167 (1992)). In addition, binding sites have been reported in a number of rat and human cell lines (e.g. Y1 in SK-N-MC, MC-IXC, CHP-212, and PC12 cells; Y2 in SK-N-Be(2), CHP-234, and SMS-MSN)(Grundemar, L., S. P. Sheikh, and C. Wahlestedt, In: The Biology of Neuropeptide Y and Related Peptides. (Humana Press, Inc., Totawa, N.J.), (1992)).
NPY forms a family (called the pancreatic polypeptide family) together with pancreatic polypeptide (PP) and peptide YY (PYY) which all consist of 36 amino acids and have a common tertiary structure, the so-called PP-fold (Glover, I. D., D. J. Barlow, J. E. Pitts, S. P. Wood, I. J. Tickle, T. L. Blundell, K. Tatemoto, J. R. Kimmel, A. Wollmer, W. Strassburger, and Y. -S. Zhang. Conformational studies of the pancreatic polypeptide. hormone family. Eur. J. Biochem. 142:379-385 (1985)). Specific features of this family include a polyproline helix in residues 1 through 8, beta -turn in residues 9 through 14, an alpha -helix in residues 15 through 30, an outward-projecting C-terminus in residues 30 through 36, and a carboxy terminal amide which appears to be critical for biological activity (Schwartz, T. W., J. Fuhlendorff, L. L. Kjems, M. S. Kristensen, M. Vervelde, M. O'Hare, J. L. Krstenansky, and B. Bjornholm. Signal epitopes in the three-dimensional structure of neuropeptide Y. Ann. N.Y. Acad. Sci. 611:35-47 (1990)). The C-terminal amidated residue of these peptides is essential for biological activity (Wahlestedt et al., 1986). Studies with peptide fragments of NPY have indicated that multiple NPY receptor subtypes exist (Wahlestedt, C., N. Yanaihara, and R. Hakanson. Evidence for different pre- and postjunctional receptors for neuropeptide Y and related peptides. Regul. Pept. 13:307-318 (1986)). Three major NPY receptor subtypes (Y1, Y2 and Y3) have been defined by pharmacological criteria, with a fourth "atypical" Y1 receptor that has been proposed to regulate feeding behavior. One of the key pharmacological features which distinguish Y1 and Y2 is the fact that the Y1 receptor (and not the Y2 receptor) responds to an analog of NPY modified at residues 31 and 34 ([Leu31,Pro34]NPY), whereas the Y2 receptor (and not the Y1 receptor) has high affinity for the NPY peptide carboxyl-terminal fragment NPY-(13-36)(Fuhlendorff, J., U. Gether, L. Aakerlund, N. Langeland-Johansen, H. Thogersen, S. G. Melberg, U. B. Olsen, O. Thastrup, and T. W. Schwartz. [Leu31,Pro34]Neuropeptide Y: A specific Y1 receptor agonist. Proc. Natl. Acad. Sci. USA 87:182-186 (1990)).
Experimental and clinical observations have supported the concept that neuropeptides play central roles in neurotransmission as well as the regulation of secretory functions of adenohypophysial, pancreatic, adrenalcortical and gut cells. Among the thirty or so neuropeptides that have been implicated in neuronal function in the mammalian central nervous system, several have also been suggested to function as neurotransmitters or neuromodulators primarily in afferent neurons.
An additional action of NPY is to decrease cardiac contractility (inotropy). This is an extremely important action of NPY, because it is known that, under many circumstances in which inotropy is decreased, diseases of life-threatening importance, e.g. congestive heart failure and cardiogenic shock, are associated with probable increased release of NPY into the blood. Prevention of NPY release, using a presynaptic NPY agonist, or NPY's action, using a postsynaptic NPY antagonist, may be beneficial in these disease states.
NPY has also been reported to produce coronary artery vasoconstriction and thereby may decrease myocardial blood flow resulting in myocardial ischemia. Such a circumstance can result in angina pectoris or, under more severe circumstances, may result in myocardial infarction and death. In recent years, several classes of drugs have proven effective in dilating coronary arteries to prevent such events. The use of analogs of NPY are expected to prove useful in treatment of such problems.
U.S. Pat. No. 4,297,346, Rips, discloses therapeutic agents referred to as `pseudopeptides` being formed from at least one peptide radical connected by a peptide bond to a therapeutically active molecule or derivative of a therapeutically active molecule. The therapeutic agents of the invention may be in the form of derivatives such as salts, esters and amides. The basis of action of the agents of the invention is the ability of the agents of the invention to cross bodily biological barriers because of the basically peptide structure of the agents. The invention also includes the preparation of the agents of the invention.
U.S. Pat. No. 5,328,899, Boublik et al., issued Jul. 12, 1994, discloses NPY peptide analogs. Human Neuropeptide Y (NPY) has the formula: H-Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu-Asp-Ala-Pro- Ala-Glu-Asp-Met-Ala-Arg-Tyr-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Th r-Arg-Gln-Arg -Tyr-NH2 (SEQ ID NO:1). Porcine and rat NPY have the same sequence except for Leu instead of Met in the 17-position (SEQ ID NO:2). Porcine PYY is homologous having 11 different residues. NPY analogs and N-terminally-shortened fragments, e.g. NPY(18-36), which contain one or more specific D-isomer substitutions for the naturally occurring residues (as well as pharmaceutically acceptable salts thereof), dispersed in a pharmaceutically acceptable liquid or solid carrier, can be administered to mammals, including humans, to substantially lower blood pressure over an extended period of time or to counteract hypertension.
U.S. Pat. No. 4,839,343, Waeber et al., issued Jun. 13, 1989, discloses a preparation containing hexatriacontapeptides suitable for intravenous administration to human or other animal subjects which are effective in treating life-threatening hypotension as encountered in bacteremic, anaphylactic or cardiogenic shock.
Several references have disclosed CCK agonists or analogs of CCK-8. For example, U.S. Pat. No. 4,490,364, issued Dec. 25, 1984 to Rivier, discloses heptapeptide, octapeptide and nonapeptide analogs of CCK-8 as CCK agonists for stimulating gallbladder contractions, arresting the secretion of gastric acid and treating convulsions. J. D. Rosamond in European Patent Application EP381,340, published Aug. 8, 1990, and in European Patent Application EP268,297, published May 25, 1988, discloses hepta- and octapeptides with sulfate ester groups which are useful for treating obesity.
U.S. Pat. No. 5,270,302, Shiosaki et al., issued Dec. 14, 1993, discloses derivatives of tetrapeptides as CCK agonists which are selective and potent Type-A CCK receptor agonists useful in the treatment of gastrointestinal disorders (including gallbladder disorders), central nervous system disorders, insulin-related disorders and pain, as well as in appetite regulation.
None of these references individually or collectively teach or suggest the present invention.